This invention relates to a process for removing undesired gaseous components from hot combustion gases by scrubbing with a regenerable absorption agent.
The problem of removing undesired gaseous components from combustion gases is becoming ever more pressing. The sulfurous components occurring in the combustion gases when burning fossil fuel in coal or oil based power plants in particular are damaging to the environment and therefore must be removed from the combustion gases before such are released into the atmosphere.
The removal of sulfur dioxide from such combustion gases thus far has been conducted mostly chemically, namely by scrubbing with absorption means in which the effective ingredients were alkali or alkali-earth compounds. As a rule, alkaline earth oxides or carbonates, such as magnesium oxide or calcium carbonate, or also alkali metal carbonates, alkali metal hydrogen carbonates, alkali metal sulfites, alkali metal hydrogen sulfites or alkali metal thiosulfates, or instance of sodium, have been used. The resulting reaction products are the corresponding sulfurous salts, namely sulfites, hydrogen sulfites or sulfates. These chemical absorption processes have been conducted primarily at relatively high temperatures only slightly, if at all, below the temperatures at which the combustion gases themselves were obtained. The equipment for implementing these purification processes is therefore subjected to a substantial and constant thermal load and must be made of the appropriate heat-resistant materials. Additionally, the waste gases finally expelled into the atmosphere at relatively high temperatures often still contain steam, even when part of their thermal energy had been previously tapped, for instance for the production of superheated steam or for preheating the combustion air.
As an incidental note, it is seen that Patent No. 965,919 of the Federal Republic of Germany discloses treating the gas to be purified by low temperature scrubbing, for instance with methanol at -80.degree. C., especially to remove sulfur dioxide from gases; however, this patent is irrelevant to the present invention insofar as the patent does not pertain to the treatment of hot combustion gases. Instead, the gases to be purified in this patent are initially at ambient temperature. For cooling purposes, there is provided a special ethylene coolant circulating system.